Modified karl fischer reagent

ABSTRACT

A modified Karl Fischer reagent containing, as the reducing agent, a sulphoxide or an organic nitrite of relatively low vapor pressure, and a base which is not pyridine but is a substantially odorless base containing the pyridine skeleton.

United States Patent Delmonte [451 Apr. 18, 1972 [54] MODIFIED KARLFISCHER REAGENT [72] Inventor: Clive Stephen Delmonte, 12 High Road,[56] Refgrences cued Buckhurst Hill, England UNITED STATES PATENTS [22]Filed: July 2, 1970 2,780,601 2/ 1957 Blomgren et al ..252/408 [21]APPLNOI: 52,009 2,967,155 1/1961 Blomgren et al. ..23/230RX PrimaryExamirrer-Morris O. Wolk [30] Foreign Application Priority Data AsmmmExammer-R- Reese Attorney-Woodhams, Blanchard and Flynn July 14, 1969Great Britain ..35,246/69 Dec. 6, 1969 Great Britain.... ...59,701/69[57] ABSTRACT Feb. 20 1970 Great Britain.... 347/70 A modified KarlFischer reagent containing, as the reducmg Mar. 18, 1970 Great Britain..13,126/70 agent, a sulphoxide or an organic nitrite of relatively lowvapor pressure, and a base which is not pyridine but is a substantiallyodorless base containing the pyridine skeleton. [58] 12 Claims, NoDrawings Field of Search ..23/230; 252/408 MODIFIED KARL FISCHER REAGENTThe invention relates to a reagent effective to determine, chemically,small quantities of water in various substances.

It is known that small quantities of water in various substances may bedetermined chemically with Karl Fischer reagent. The use of such reagentis of particular value where the common physical methods areinapplicable, especially for the determination of small percentages ofwater in certain liquids and in certain volatile solids.

Karl Fischer reagent is composed essentially of iodine and sulphurdioxide in pyridine/methanol solution, and its reaction with water,represented in a simple form, is as follows:

So formulated, the reagent has several disadvantages. Thus the reagentis highly malodorous and its vapor is toxic. Pyridine vapor iscarcinogenic and sulphur dioxide vapor is now known to cause geneticdefects. The reagent is hygroscopic and is attacked by oxygen, andconsequently it deteriorates on exposure to the atmosphere. The reagentthus requires to be handled under dry nitrogen or other dry, inert gas.The reagent is also sensitive to light and tends to age rapidly even incomparative darkness.

It is an object of the invention to provide a modified reagent of theKarl Fischer type in which one or more of the foregoing disadvantagesare mitigated.

According to the invention, the reagent contains a reducing agent otherthan sulphur dioxide and, instead of pyridine, a substantially odorlessorganic base of relatively low volatility.

The reducing agent, which replaces the sulphur dioxide of the KarlFischer reagent, suitably has a relatively low vapor pressure at roomtemperature (20 C) and is advantageously a sulphoxide or an organicnitrite. The preferred sulphoxides are dialkyl sulphoxides in whicheachalkyl group contains not more than four carbon atoms, particularlydimethyl sulphoxide (DMSO). In the spent reagent, the sulphoxide isoxidized to the sulphone. Suitable nitrites include alkyl nitritescontaining at least four carbon atoms in the alkyl group, the preferrednitrites being the butyl and amyl nitrites, for example, n-butyl,isobutyl, n-amyl and isoamyl nitrites. The equation of the reaction withwater ofthe reagent containing a nitrite is as follows The base, whichhas a relatively low vapor pressure at room temperature (20 C),preferably contains the pyridine nucleus or skeleton and it may be asolid or a high-boiling liquid, for example, a liquid having a boilingpoint in the range l50-300 CQThe base may be a bipyridyl, a polypyridyl,a biquinolyl, a 2-(pyridyl)propane-( 1,3)-diol or a 2-(pyridyl)-tertiarybutane-( l,3,4)-tn'ol, for example the 27-pyridyl compounds. Thesehydroxylic bases are amongst the preferred bases for use in the reagentaccording to the invention; they may be prepared by the method describedby Lipp and Zimgibl, Chemische Berichte 1906), 39, 1045-1054.

The oxidizing agent in the reagent is preferably iodine. However, a partof the iodine may be replaced by a compound of a polyvalent metal in ahigher state of oxidation, for example a ferric or cupric compound,suitably ferric thiocyanate or anhydrous cupric salicylate. The mode ofaction of a reagent containing oxidizing ions of a metal (M,) of chargen is as follows:

A preferred reagent contains, per liter, 0.05l.0 mole free iodine or anequivalent amount of a mixture of free iodine and a compound of a metalin a high oxidation state; 0.1-2.0 moles of a sulphoxide or nitrite,particularly dimethyl sulphoxide, butyl nitrite or amyl nitrite; and0.1-4.0 moles of a substantially odorless organic base of lowvolatility, particularly a base incorporating a pyridine nucleus.

The solvent used in the reagent is preferably a hydroxylic compound,particularly methanol. Other suitable solvents include ethanol, ethyleneglycol, diethylene glycol and dioxan.

The reagent may, when necessary, include a compound effective as acatalyst to promote the reaction of the reagent with water. Thecatalytic compound is preferably a strong organic base, a suitablecatalyst being N-ethylpiperidine. Tri-nbutylamine is also a suitablecatalyst. When a catalyst is used, it may be added to the sample undertest rather than directly to the reagent.

To mitigate or prevent oxidation of the reagent and to hinderhygroscopic absorption of water by the reagent, the reagent may beprovided with a protective, surface film. Preferred surface films ofthis kind may be formed by (1) normally liquid silicones having aviscosity which is preferably below 3 centistokes and/or a specificgravity preferably below 0.90, or a methyl phenyl silicone preferablybelow 100 centistokes, or (2) a surfactant of low solubility in thereagent solvent, the preferred surfactants being long chain alkylbenzenesulphonates.

The presence of certain ions, typically K*, Na, Sr, Co", Zn and I, invarying degrees, catalyze, accelerate or promote the reaction, stabilizethe reagent and improve its end-point and one or more of them may beincluded in the reagent. The metal ions may, for example, be introducedas acetates and the iodide ion as, for example, pyridinium iodide orpotassium iodide. Certain indicators, widely used in nonaqueouschemistry, can be added to the reagent, or to the sample under test, tosharpen the'end-point, especially if the endpoint at a particular pH isrequired. Suitable indicators include acn'dine and thymol blue.

The reagent according to the invention can be used to determine thewater content of miscellaneous substances, in the manner known with theKarl Fischer reagent. Typical examples of such use include thedetennination of the water content (a) of oils, fats and greases; (b) ofwheat and of foodstuffs generally; and (c) of organic and inorganichydrates. The reagent may also be used to determine the rate of achemical reaction when water is generated in that reaction.

It will be understood that the invention also includes the use of thereagent in the determination of the water content of substances.

The invention is illustrated in the following examples.

EXAMPLE 1 The reagent consisted of a solution in methanol of Dimethylsulphoxide 25 g per liter Iodine 75 g per liter Bipyridyl (an unresolvedmixture of isomers, including the 2-2' and 2-3 isomers) 50 g per literN-ethylpiperidine 25 ml per liter A droplet of a methyl phenyl siliconehaving a viscosity at 25 C of about centistokes was added to a liter ofthe reagent to form a surface film.

EXAMPLE 2 The reagent had the same composition as in Example 1 exceptthat the catalyst, N-ethylpiperidine, was omitted. When necessary, anappropriate amount of the catalyst was added to the reaction vessel inwhich the water content of the sample under test was being determined.

EXAMPLE 3 The reagent had the same composition as in Example 1 exceptthat the catalyst was tri-n-butylamine.

EXAMPLE 4 The reagent consisted of a solution in methanol of EXAMPLE 5The reagent consisted of the methanol solution specified in Example 4but there was added to 1 liter of the solution a drop of a silicone toform a protective, surface film.

EXAMPLES 6a 6d Four reagents were produced corresponding, respectively,to the reagents of Examples 1, 2, 3 and except that the silicone surfacefilm was replaced by a film of sodium dodecylbenzene sulphonate.

lclaim:

1. In a reagent of the Karl Fischer type for the determination of smallquantities of water in various substances, the improvement in which lthe reducing agent is a member of the group consisting of sulphoxidesand organic nitrites of relatively low vapor pressure at 20 C and (2)the base is not pyridine but is a substantially odorless base containingthe pyridine skeleton and having a relatively low vapor pressure at 20C.

2. A reagent according to claim 1, in which the reducing agent is amember of the group consisting of dimethyl sulphoxide, butyl nitritesand amyl nitrites.

3. A reagent according to claim 2, in which the said base is a member ofthe group consisting of bipyridyls, polypyridyls, biquinolyls,2-(pyridyl)-propane-(1,3)-diols and 2-(pyridyl)- tertiary butane-(l,3,4)-triols.

4. A reagent according to claim 3 including, as oxidizing agent, amixture of free iodine and a compound of a polyvalent metal in'a higherstate of oxidation.

5. A reagent according to claim 4, in which said polyvalent metalcompound is a member of the group consisting of ferric and cupriccompounds.

6. A reagent according to claim 3, including free iodine as oxidizingagent.

7. A reagent according to claim 6, containing 005-1 .0 mole per liter offree iodine, 0.1-2.0 moles per liter of reducing agent and 0.1-4.0 molesper liter of said base.

8. A reagent according to claim 7, in which the solvent is methanol.

9. A reagent according to claim 7, including a catalytic amount of asubstance effective to promote the reaction of the reagent with water,said substance being a strong, organic ase.

10. A reagent according to claim 7, including a surface film effectiveto mitigate aerial oxidation of the reagent and hygroscopic absorptionof water by the reagent.

11. A reagent according to claim 10, in which the surface film is formedby a member of the group consisting of normally liquid silicones andsurfactants of low solubility in organic, hydroxylic solvent.

12. A process of determining small quantities of water in varioussubstances by the Karl Fischer method in which the reagent employed isthat claimed in claim 1.

2. A reagent according to claim 1, in which the reducing agent is amember of the group consisting of dimethyl sulphoxide, butyl nitritesand amyl nitrites.
 3. A reagent according to claim 2, in which the saidbase is a member of the group consisting of bipyridyls, polypyridyls,biquinolyls, 2-(pyridyl)-propane-(1,3)-diols and 2-(pyridyl)-tertiarybutane-(1,3,4)-triols.
 4. A reagent according to claim 3 including, asoxidizing agent, a mixture of free iodine and a compound of a polyvalentmetal in a higher state of oxidation.
 5. A reagent according to claim 4,in which said polyvalent metal compound is a member of the groupconsisting of ferric and cupric compounds.
 6. A reagent according toclaim 3, including free iodine as oxidizing agent.
 7. A reagentaccording to claim 6, containing 0.05-1.0 mole per liter of free iodine,0.1-2.0 moles per liter of reducing agent and 0.1-4.0 moles per liter ofsaid base.
 8. A reagent according to claim 7, in which the solvent ismethanol.
 9. A reagent according to claim 7, including a catalyticamount of a substance effective to promote the reaction of the reagentwith water, said substance being a strong, organic base.
 10. A reagentaccording to claim 7, including a surface film effective to mitigateaerial oxidation of the reagent and hygroscopic absorption of water bythe reagent.
 11. A reagent according to claim 10, in which the surfacefilm is formed by a member of the group consisting of normally liquidsilicones and surfactants of low solubility in organic, hydroxylicsolvent.
 12. A process of determining small quantities of water invarious substances by the Karl Fischer method in which the reagentemployed is that claimed in claim 1.